The overall purpose of this proposal is to determine if testicular recrudescence in hamsters can be utilized as a model of puberty with reference to changes in Sertoli cell function. Hamsters offer the advantage that testicular function is both normally and reversibly modified by changes in photoperiod which are presumably due to changes in pineal gland activity. Sertoli cells from immature, normal adult (i.e. 14:10 light cycle) and adult hamsters undergoing photoperiod-induced testicular regression (i.e. 8:16 light cycle) and recrudescence will be purified and cultured. Changes in Sertoli cell function during normal puberty and photoperiod-induced testicular regression and recrudescence will be monitored by the measurement of changes in the ability of FSH to stimulate cyclic AMP accumulation. The mechanism of the changes in Sertoli cell responsiveness to FSH during normal puberty and the recrudescence phase of photoperiod-induced testicular regression and recrudescence will be assessed by measurement of hormone binding and changes in the cyclic nucleotide system. If both the changes in FSH responsiveness and the mechanism of these changes is the same during the initiation of puberty and testicular recrudescence, then as far as the Sertoli cell is concerned the photoperiod-induced changes can be utilized as a model of puberty. The use of this model system will then allow more extensive studies on the role of hormones (FSH, LH, prolactin, testosterone) in the changes in FSH responsiveness during puberty and the physiological mechanism responsible for them.